/**
 * Work-order import — value mapping (issue #415, step 2 of 3, layer 2 of 2).
 *
 * Layer 1 (`./columnMapping`) said which column is the workstream. This layer
 * says which of *that column's values* is which of the project's workstreams —
 * and then, scoped to each of those, which contractor and which stage.
 *
 * ## The scoping rule (ADR-0019)
 *
 * A contractor value does not map to "a contractor"; it maps to a contractor
 * **assigned to that row's workstream** (`project_workstream_contractor`), and
 * a stage maps to a stage on **that workstream's own ladder**
 * (`project_workstream_stage`). The same text can therefore need two different
 * answers — "Acme" under Windows is a different assignment from "Acme" under
 * Doors, and may not exist at all under one of them. So contractor and stage
 * entries are keyed by `(resolved workstream, value)`, never by value alone,
 * and each offers only that workstream's assignments.
 *
 * A consequence worth stating: rows whose workstream value is blank or not yet
 * mapped have no scope, so their contractor and stage values cannot be listed
 * yet. They are counted (`unscopedRows`) rather than guessed at, and appear as
 * soon as their workstream is mapped — which is why the whole model is derived
 * fresh from `(rows, columnMapping, valueMapping, targets)` on every change
 * instead of being accumulated in state.
 *
 * ## One-to-one vs many-to-one
 *
 * Column mapping is one-to-one (one column per field), so it assigns greedily.
 * Value mapping is deliberately **many-to-one**: "Window Programme" and
 * "Windows - Phase 2" may both be the Windows workstream, so each distinct
 * value takes its own best match independently.
 *
 * ## What blocks what
 *
 * Nothing here blocks progression to validation — that is column mapping's job.
 * An unmapped value is a *warning* whose rows become validation errors at #417,
 * except a blank Stage, which is legitimate and falls back to the workstream's
 * first stage at commit.
 *
 * Pure and DB-free.
 */

import {
  normaliseForMatch,
  VALUE_MATCH_THRESHOLD,
  valueSimilarity,
} from "./similarity";
import { cellFor, type ImportColumnMapping } from "./columnMapping";
import type { ImportMappingTargets, WorkstreamTarget } from "./mappingTargets";

/**
 * The user's value-level decisions.
 *
 * A key that is **absent** has never been touched, so auto-match speaks for it.
 * A key mapped to **null** was explicitly cleared, and auto-match must not
 * quietly put its suggestion back — "I looked at this and none of them is
 * right" is an answer.
 *
 * Contractor and stage keys carry their workstream scope (see `scopedValueKey`).
 */
export interface ImportValueMapping {
  /** value key → `project_workstream.id`. */
  workstreams: Record<string, string | null>;
  /** scoped key → `project_workstream_contractor.id`. */
  contractors: Record<string, string | null>;
  /** scoped key → `project_workstream_stage.id`. */
  stages: Record<string, string | null>;
}

export const EMPTY_VALUE_MAPPING: ImportValueMapping = {
  workstreams: {},
  contractors: {},
  stages: {},
};

/**
 * The key a file value is remembered by: its normalised form, so "ACME LTD",
 * "Acme Ltd" and "acme  ltd" are one decision rather than three.
 */
export function valueKey(value: string): string {
  return normaliseForMatch(value);
}

/** The key a contractor/stage value is remembered by, within one workstream. */
export function scopedValueKey(
  projectWorkstreamId: string,
  value: string,
): string {
  // The workstream id is all digits (a `bigserial`), so the first space is
  // unambiguously the separator however many spaces the value itself carries.
  return `${projectWorkstreamId} ${valueKey(value)}`;
}

export type ValueMappingStatus = "matched" | "needs_review";

/** Where a mapped value's answer came from — the UI badges auto-matches. */
export type ValueMatchSource = "user" | "auto" | null;

export interface WorkstreamValueEntry {
  /** The value as it first appears in the file, for display. */
  value: string;
  /** Its `valueKey`, for reading and writing `ImportValueMapping.workstreams`. */
  key: string;
  /** How many file rows carry this value. */
  rowCount: number;
  /** `project_workstream.id`, or null when unmapped. */
  targetId: string | null;
  matchedBy: ValueMatchSource;
  status: ValueMappingStatus;
}

export interface ScopedValueEntry {
  /** The workstream this decision is scoped to — the row's mapped workstream. */
  workstreamId: string;
  workstreamName: string;
  value: string;
  /** Its `scopedValueKey`, for reading and writing the mapping. */
  key: string;
  rowCount: number;
  /** `project_workstream_contractor.id` / `project_workstream_stage.id`, or null. */
  targetId: string | null;
  matchedBy: ValueMatchSource;
  status: ValueMappingStatus;
  /**
   * True when the workstream this value sits under has nothing to offer — no
   * contractor assigned, or no stage on its ladder. The readiness gate
   * (ADR-0019) makes this unreachable from the import page, but a caller that
   * skipped the gate would otherwise show an empty picker with no explanation.
   */
  noTargets: boolean;
}

export interface ValueMappingModel {
  /** Distinct workstream values, biggest row count first. */
  workstreams: WorkstreamValueEntry[];
  /** Distinct (workstream, contractor value) pairs, biggest row count first. */
  contractors: ScopedValueEntry[];
  /** Distinct (workstream, stage value) pairs. Blank stage cells are not listed. */
  stages: ScopedValueEntry[];
  /** Whether the column behind each value table is mapped at all. */
  hasWorkstreamColumn: boolean;
  hasContractorColumn: boolean;
  hasStageColumn: boolean;
  /** Rows whose cell is blank, per field. A blank stage is legitimate; the others are not. */
  blankRows: { workstream: number; contractor: number; stage: number };
  /**
   * Rows carrying a workstream value that is not yet mapped, so their
   * contractor and stage values cannot be scoped and are not listed yet. They
   * appear as soon as that workstream value is mapped — which is what separates
   * them from rows whose workstream cell is simply blank (`blankRows`).
   */
  unscopedRows: number;
  /** Entries still needing review, per table. */
  needsReview: { workstreams: number; contractors: number; stages: number };
  /**
   * Rows that will fail validation at #417 as things stand: a blank or unmapped
   * workstream, a blank or unmapped contractor, or a *provided* stage that
   * matches nothing. Counted per row, so a row with two problems counts once.
   */
  warningRows: number;
}

/** Row-level view of one file row's three mappable values. */
interface RowValues {
  workstream: string;
  contractor: string;
  stage: string;
}

/**
 * Build the whole value-mapping picture from the file, the column mapping, the
 * user's value decisions and the project's targets.
 *
 * One pass over the rows to count distinct values, then a second, tiny pass
 * over the distinct sets to resolve each. It is re-run on every edit — the
 * inputs are small enough (20,000 rows at most, three cells each) that deriving
 * beats caching, and caching is what would let the tables disagree with the
 * mapping the user is looking at.
 */
export function buildValueMappingModel(
  rows: string[][],
  columnMapping: ImportColumnMapping,
  valueMapping: ImportValueMapping,
  targets: ImportMappingTargets,
): ValueMappingModel {
  const hasWorkstreamColumn = columnMapping.fields.workstream !== undefined;
  const hasContractorColumn = columnMapping.fields.contractor !== undefined;
  const hasStageColumn = columnMapping.fields.stage !== undefined;

  const blankRows = { workstream: 0, contractor: 0, stage: 0 };

  // Pass 1 — distinct workstream values, and the contractor/stage values seen
  // beneath each of them (keyed by the *file's* workstream value, since the
  // workstream it resolves to is not known until pass 2).
  const workstreamValues = new Map<string, { value: string; rowCount: number }>();
  const rowsByWorkstreamKey = new Map<string, RowValues[]>();

  for (const row of rows) {
    const values: RowValues = {
      workstream: cellFor(row, columnMapping, "workstream"),
      contractor: cellFor(row, columnMapping, "contractor"),
      stage: cellFor(row, columnMapping, "stage"),
    };

    if (values.workstream === "") blankRows.workstream++;
    if (values.contractor === "") blankRows.contractor++;
    if (values.stage === "") blankRows.stage++;

    if (values.workstream === "") continue;

    const key = valueKey(values.workstream);
    const seen = workstreamValues.get(key);
    if (seen) seen.rowCount++;
    else workstreamValues.set(key, { value: values.workstream, rowCount: 1 });

    const bucket = rowsByWorkstreamKey.get(key);
    if (bucket) bucket.push(values);
    else rowsByWorkstreamKey.set(key, [values]);
  }

  // Pass 2 — resolve each distinct workstream value.
  const workstreams: WorkstreamValueEntry[] = [];
  const resolvedByKey = new Map<string, WorkstreamTarget>();
  const targetsById = new Map(targets.workstreams.map((w) => [w.id, w]));

  for (const [key, { value, rowCount }] of workstreamValues) {
    const resolved = resolveValue(
      key,
      value,
      valueMapping.workstreams,
      targets.workstreams,
      (target) => target.name,
      (target) => target.id,
    );
    workstreams.push({ value, key, rowCount, ...resolved });
    const target = resolved.targetId
      ? targetsById.get(resolved.targetId)
      : undefined;
    if (target) resolvedByKey.set(key, target);
  }

  // Pass 3 — contractor and stage values, grouped by the workstream their rows
  // resolved to. Two file spellings of the same workstream merge here, which is
  // right: they are one workstream, so "Acme" beneath either is one decision.
  const contractorTally = new Map<
    string,
    { workstream: WorkstreamTarget; value: string; rowCount: number }
  >();
  const stageTally = new Map<
    string,
    { workstream: WorkstreamTarget; value: string; rowCount: number }
  >();
  // Rows with a *blank* workstream are reported as blank, not as unscoped:
  // mapping cannot rescue them, so promising that their contractors will appear
  // once the workstream is mapped would be a lie.
  let unscopedRows = 0;

  for (const [key, bucket] of rowsByWorkstreamKey) {
    const workstreamTarget = resolvedByKey.get(key);
    if (!workstreamTarget) {
      // Unmapped workstream: no scope, so nothing beneath it can be listed yet.
      unscopedRows += bucket.length;
      continue;
    }
    for (const values of bucket) {
      if (hasContractorColumn && values.contractor !== "") {
        tally(contractorTally, workstreamTarget, values.contractor);
      }
      // A blank stage is legitimate — it falls back to the workstream's first
      // stage at commit — so it is counted as blank, never listed for mapping.
      if (hasStageColumn && values.stage !== "") {
        tally(stageTally, workstreamTarget, values.stage);
      }
    }
  }

  const contractors = [...contractorTally.entries()].map(
    ([key, { workstream, value, rowCount }]) => ({
      workstreamId: workstream.id,
      workstreamName: workstream.name,
      value,
      key,
      rowCount,
      noTargets: workstream.contractors.length === 0,
      ...resolveValue(
        key,
        value,
        valueMapping.contractors,
        workstream.contractors,
        (target) => target.name,
        (target) => target.id,
      ),
    }),
  );

  const stages = [...stageTally.entries()].map(
    ([key, { workstream, value, rowCount }]) => ({
      workstreamId: workstream.id,
      workstreamName: workstream.name,
      value,
      key,
      rowCount,
      noTargets: workstream.stages.length === 0,
      ...resolveValue(
        key,
        value,
        valueMapping.stages,
        workstream.stages,
        (target) => target.name,
        (target) => target.id,
      ),
    }),
  );

  byRowCount(workstreams);
  byRowCount(contractors);
  byRowCount(stages);

  return {
    workstreams,
    contractors,
    stages,
    hasWorkstreamColumn,
    hasContractorColumn,
    hasStageColumn,
    blankRows,
    unscopedRows,
    needsReview: {
      workstreams: workstreams.filter((e) => e.status === "needs_review").length,
      contractors: contractors.filter((e) => e.status === "needs_review").length,
      stages: stages.filter((e) => e.status === "needs_review").length,
    },
    warningRows: countWarningRows(
      rowsByWorkstreamKey,
      resolvedByKey,
      blankRows.workstream,
      new Set(
        contractors.filter((e) => e.status === "needs_review").map((e) => e.key),
      ),
      new Set(
        stages.filter((e) => e.status === "needs_review").map((e) => e.key),
      ),
    ),
  };
}

/** Add one row's contribution to a scoped tally. */
function tally(
  into: Map<
    string,
    { workstream: WorkstreamTarget; value: string; rowCount: number }
  >,
  workstream: WorkstreamTarget,
  value: string,
): void {
  const key = scopedValueKey(workstream.id, value);
  const seen = into.get(key);
  if (seen) seen.rowCount++;
  else into.set(key, { workstream, value, rowCount: 1 });
}

/**
 * Decide one value: the user's answer if they gave one, otherwise the best
 * target above the auto-match threshold, otherwise nothing.
 *
 * A user answer that names a target no longer on offer (they mapped a
 * contractor, then re-pointed the workstream at one that contractor is not
 * assigned to) is discarded rather than kept as a dangling id — the value falls
 * back to needing review, which is the truth of the situation.
 */
function resolveValue<T>(
  key: string,
  value: string,
  decisions: Record<string, string | null>,
  candidates: readonly T[],
  nameOf: (target: T) => string,
  idOf: (target: T) => string,
): { targetId: string | null; matchedBy: ValueMatchSource; status: ValueMappingStatus } {
  if (Object.prototype.hasOwnProperty.call(decisions, key)) {
    const chosen = decisions[key];
    if (chosen === null) {
      return { targetId: null, matchedBy: null, status: "needs_review" };
    }
    if (candidates.some((target) => idOf(target) === chosen)) {
      return { targetId: chosen, matchedBy: "user", status: "matched" };
    }
    return { targetId: null, matchedBy: null, status: "needs_review" };
  }

  let best: { id: string; score: number } | null = null;
  let tied = false;
  for (const target of candidates) {
    const score = valueSimilarity(value, nameOf(target));
    if (score < VALUE_MATCH_THRESHOLD) continue;
    if (best === null || score > best.score) {
      best = { id: idOf(target), score };
      tied = false;
    } else if (score === best.score) {
      tied = true;
    }
  }

  // Two candidates the value fits equally well is not a match, it is a
  // question: "Acme" beneath a workstream carrying both Acme Windows and Acme
  // Doors must be asked, not guessed. (ADR-0019 leaves same-org disambiguation
  // to #417; this keeps the guess from being made here in the meantime.)
  return best && !tied
    ? { targetId: best.id, matchedBy: "auto", status: "matched" }
    : { targetId: null, matchedBy: null, status: "needs_review" };
}

/** Biggest first, then alphabetical — stable as the user maps, since neither key changes. */
function byRowCount(entries: Array<{ rowCount: number; value: string }>): void {
  entries.sort(
    (a, b) => b.rowCount - a.rowCount || a.value.localeCompare(b.value, "en-GB"),
  );
}

/**
 * How many rows will fail validation at #417 as things stand.
 *
 * Counted **per row**, by walking the rows again rather than by summing the
 * tables' row counts: a row with an unmapped workstream *and* a blank
 * contractor is one broken row, not two, and summing the tables would report it
 * twice.
 *
 * A row is broken when its workstream is blank or unmapped, its contractor is
 * blank or unmapped, or it carries a stage that matches nothing. A *blank*
 * stage is not broken — it falls back to the workstream's first stage.
 */
function countWarningRows(
  rowsByWorkstreamKey: Map<string, RowValues[]>,
  resolvedByKey: Map<string, WorkstreamTarget>,
  blankWorkstreamRows: number,
  unmappedContractorKeys: Set<string>,
  unmappedStageKeys: Set<string>,
): number {
  // A blank workstream cell is unmappable, so every such row is already broken.
  let broken = blankWorkstreamRows;

  for (const [key, bucket] of rowsByWorkstreamKey) {
    const workstream = resolvedByKey.get(key);
    if (!workstream) {
      // The whole bucket shares one unmapped workstream value.
      broken += bucket.length;
      continue;
    }
    for (const values of bucket) {
      const contractorBroken =
        values.contractor === "" ||
        unmappedContractorKeys.has(scopedValueKey(workstream.id, values.contractor));
      const stageBroken =
        values.stage !== "" &&
        unmappedStageKeys.has(scopedValueKey(workstream.id, values.stage));
      if (contractorBroken || stageBroken) broken++;
    }
  }

  return broken;
}

/** Record one workstream-value decision. `null` means "none of these". */
export function setWorkstreamValue(
  mapping: ImportValueMapping,
  key: string,
  targetId: string | null,
): ImportValueMapping {
  return {
    ...mapping,
    workstreams: { ...mapping.workstreams, [key]: targetId },
  };
}

/** Record one contractor decision, scoped to its workstream. */
export function setContractorValue(
  mapping: ImportValueMapping,
  key: string,
  targetId: string | null,
): ImportValueMapping {
  return {
    ...mapping,
    contractors: { ...mapping.contractors, [key]: targetId },
  };
}

/** Record one stage decision, scoped to its workstream. */
export function setStageValue(
  mapping: ImportValueMapping,
  key: string,
  targetId: string | null,
): ImportValueMapping {
  return { ...mapping, stages: { ...mapping.stages, [key]: targetId } };
}