import { normalizePdfContentText } from "./text.js";
import type {
  PdfBasicComparison,
  PdfDocumentSnapshot,
  PdfPagePair,
  VisualDiffIssue,
  VisualDiffThresholds,
} from "./types.js";

export const DEFAULT_VISUAL_DIFF_THRESHOLDS: VisualDiffThresholds = {
  pageSizeDeltaPt: 0.5,
  contentSimilarity: 0.999,
  strictPageCount: true,
  pixelDifferenceThreshold: 8,
  maxMeanAbsoluteError: 8,
  maxChangedPixelRatio: 0.05,
  minInkIou: 0.75,
  minEdgeIou: 0.6,
};

function cappedLevenshteinDistance(
  left: string,
  right: string,
  cap: number,
): number {
  if (left === right) {
    return 0;
  }
  if (Math.abs(left.length - right.length) > cap) {
    return cap + 1;
  }
  let previous = new Int32Array(right.length + 1);
  let current = new Int32Array(right.length + 1);
  for (let column = 0; column <= right.length; column += 1) {
    previous[column] = column;
  }
  for (let row = 1; row <= left.length; row += 1) {
    current.fill(cap + 1);
    current[0] = row;
    const start = Math.max(1, row - cap);
    const end = Math.min(right.length, row + cap);
    let rowMinimum = cap + 1;
    for (let column = start; column <= end; column += 1) {
      const substitutionCost =
        left.charCodeAt(row - 1) === right.charCodeAt(column - 1) ? 0 : 1;
      const value = Math.min(
        (previous[column] ?? cap + 1) + 1,
        (current[column - 1] ?? cap + 1) + 1,
        (previous[column - 1] ?? cap + 1) + substitutionCost,
      );
      current[column] = value;
      rowMinimum = Math.min(rowMinimum, value);
    }
    if (rowMinimum > cap) {
      return cap + 1;
    }
    [previous, current] = [current, previous];
  }
  return Math.min(previous[right.length] ?? cap + 1, cap + 1);
}

export function calculateContentSimilarity(
  leftInput: string,
  rightInput: string,
  requiredSimilarity = DEFAULT_VISUAL_DIFF_THRESHOLDS.contentSimilarity,
): number {
  const left = normalizePdfContentText(leftInput);
  const right = normalizePdfContentText(rightInput);
  const maximumLength = Math.max(left.length, right.length);
  if (maximumLength === 0) {
    return 1;
  }
  const cap = Math.max(
    1,
    Math.ceil(maximumLength * (1 - requiredSimilarity)),
  );
  const distance = cappedLevenshteinDistance(left, right, cap);
  return Math.max(0, 1 - distance / maximumLength);
}

function createPagePairs(
  baseline: PdfDocumentSnapshot,
  candidate: PdfDocumentSnapshot,
): PdfPagePair[] {
  const pairCount = Math.max(baseline.pageCount, candidate.pageCount);
  return Array.from({ length: pairCount }, (_, index) => {
    const baselinePageNumber =
      index < baseline.pageCount ? index + 1 : undefined;
    const candidatePageNumber =
      index < candidate.pageCount ? index + 1 : undefined;
    if (baselinePageNumber === undefined) {
      if (candidatePageNumber === undefined) {
        throw new Error("页面配对状态无效");
      }
      return {
        candidatePageNumber,
        status: "candidate-only" as const,
      };
    }
    if (candidatePageNumber === undefined) {
      return {
        baselinePageNumber,
        status: "baseline-only" as const,
      };
    }
    return {
      baselinePageNumber,
      candidatePageNumber,
      status: "paired" as const,
    };
  });
}

export function comparePdfSnapshotsBasic(
  baseline: PdfDocumentSnapshot,
  candidate: PdfDocumentSnapshot,
  thresholdOverrides: Partial<VisualDiffThresholds> = {},
): PdfBasicComparison {
  const thresholds = {
    ...DEFAULT_VISUAL_DIFF_THRESHOLDS,
    ...thresholdOverrides,
  };
  const issues: VisualDiffIssue[] = [];
  const pagePairs = createPagePairs(baseline, candidate);

  if (baseline.pageCount !== candidate.pageCount) {
    issues.push({
      code: "PAGE_COUNT_MISMATCH",
      severity: thresholds.strictPageCount ? "failure" : "warning",
      message: `页数不一致：基线 ${baseline.pageCount} 页，候选 ${candidate.pageCount} 页`,
      details: {
        baselinePageCount: baseline.pageCount,
        candidatePageCount: candidate.pageCount,
      },
    });
  }

  for (const pair of pagePairs) {
    if (pair.status === "baseline-only") {
      issues.push({
        code: "UNPAIRED_BASELINE_PAGE",
        severity: "failure",
        message: `基线第 ${pair.baselinePageNumber} 页没有候选配对页`,
        baselinePageNumber: pair.baselinePageNumber,
      });
      continue;
    }
    if (pair.status === "candidate-only") {
      issues.push({
        code: "UNPAIRED_CANDIDATE_PAGE",
        severity: "failure",
        message: `候选第 ${pair.candidatePageNumber} 页为溢出页`,
        candidatePageNumber: pair.candidatePageNumber,
      });
      continue;
    }
    const baselinePage = baseline.pages[pair.baselinePageNumber - 1];
    const candidatePage = candidate.pages[pair.candidatePageNumber - 1];
    if (!baselinePage || !candidatePage) {
      continue;
    }
    const widthDelta = Math.abs(
      baselinePage.widthPt - candidatePage.widthPt,
    );
    const heightDelta = Math.abs(
      baselinePage.heightPt - candidatePage.heightPt,
    );
    if (
      widthDelta > thresholds.pageSizeDeltaPt ||
      heightDelta > thresholds.pageSizeDeltaPt
    ) {
      issues.push({
        code: "PAGE_SIZE_MISMATCH",
        severity: "failure",
        message: `第 ${pair.baselinePageNumber} 页纸张尺寸偏差超限`,
        baselinePageNumber: pair.baselinePageNumber,
        candidatePageNumber: pair.candidatePageNumber,
        details: { widthDeltaPt: widthDelta, heightDeltaPt: heightDelta },
      });
    }
    const baselineLandscape =
      baselinePage.widthPt > baselinePage.heightPt;
    const candidateLandscape =
      candidatePage.widthPt > candidatePage.heightPt;
    if (baselineLandscape !== candidateLandscape) {
      issues.push({
        code: "PAGE_ORIENTATION_MISMATCH",
        severity: "failure",
        message: `第 ${pair.baselinePageNumber} 页方向不一致`,
        baselinePageNumber: pair.baselinePageNumber,
        candidatePageNumber: pair.candidatePageNumber,
      });
    }
  }

  const contentSimilarity = calculateContentSimilarity(
    baseline.contentText,
    candidate.contentText,
    thresholds.contentSimilarity,
  );
  if (contentSimilarity < thresholds.contentSimilarity) {
    issues.push({
      code: "CONTENT_MISMATCH",
      severity: "failure",
      message: `正文文本相似度 ${(contentSimilarity * 100).toFixed(3)}% 低于门限 ${(thresholds.contentSimilarity * 100).toFixed(3)}%`,
      details: { contentSimilarity },
    });
  }

  const status = issues.some((issue) => issue.severity === "failure")
    ? "failed"
    : issues.length > 0
      ? "warning"
      : "passed";
  return {
    schemaVersion: 1,
    status,
    baseline: baseline.source,
    candidate: candidate.source,
    thresholds,
    contentSimilarity,
    pagePairs,
    issues,
  };
}