troutbot/src/engine/quality.ts

import type {
  AnalysisResult,
  EngineBackend,
  QualityBackendConfig,
  WebhookEvent,
} from '../types.js';

// Conventional commit prefixes
const CONVENTIONAL_COMMIT =
  /^(feat|fix|docs|style|refactor|perf|test|build|ci|chore|revert)(\(.+\))?!?:\s/i;

const WIP_PATTERN = /\b(wip|work.in.progress|do.not.merge|don't.merge|draft)\b/i;
const BREAKING_PATTERN = /\b(breaking.change|BREAKING)\b/i;
const TODO_PATTERN = /\b(TODO|FIXME|HACK|XXX|TEMP)\b/;

export class QualityBackend implements EngineBackend {
  name = 'quality';

  constructor(private config: QualityBackendConfig) {}

  async analyze(event: WebhookEvent): Promise<AnalysisResult> {
    const body = event.body.trim();
    const title = event.title.trim();
    const signals: { name: string; positive: boolean; weight: number }[] = [];

    // --- Title analysis ---

    if (title.length < 10) {
      signals.push({ name: 'very short title', positive: false, weight: 1.2 });
    } else if (title.length > 200) {
      signals.push({
        name: 'excessively long title',
        positive: false,
        weight: 0.5,
      });
    }

    if (CONVENTIONAL_COMMIT.test(title)) {
      signals.push({
        name: 'conventional commit format',
        positive: true,
        weight: 1,
      });
    }

    if (WIP_PATTERN.test(title) || WIP_PATTERN.test(body)) {
      signals.push({
        name: 'marked as work-in-progress',
        positive: false,
        weight: 1.5,
      });
    }

    // --- Body analysis ---

    if (body.length === 0) {
      signals.push({ name: 'empty description', positive: false, weight: 2 });
    } else if (body.length < this.config.minBodyLength) {
      signals.push({
        name: `short description (${body.length} chars)`,
        positive: false,
        weight: 1.2,
      });
    } else if (body.length >= this.config.minBodyLength) {
      signals.push({ name: 'adequate description', positive: true, weight: 1 });
      if (body.length > 300) {
        signals.push({
          name: 'thorough description',
          positive: true,
          weight: 0.5,
        });
      }
    }

    if (/```[\s\S]*?```/.test(body)) {
      signals.push({ name: 'has code blocks', positive: true, weight: 0.7 });
    }

    if (/^#{1,6}\s/m.test(body)) {
      signals.push({
        name: 'has section headers',
        positive: true,
        weight: 0.8,
      });
    }

    // Checklists
    const checklistItems = body.match(/^[\s]*-\s*\[[ x]\]/gm);
    if (checklistItems) {
      const checked = checklistItems.filter((i) => /\[x\]/i.test(i)).length;
      const total = checklistItems.length;
      if (total > 0 && checked === total) {
        signals.push({
          name: `checklist complete (${total}/${total})`,
          positive: true,
          weight: 1,
        });
      } else if (total > 0) {
        signals.push({
          name: `checklist incomplete (${checked}/${total})`,
          positive: false,
          weight: 0.8,
        });
      }
    }

    // Breaking changes
    if (BREAKING_PATTERN.test(title) || BREAKING_PATTERN.test(body)) {
      // Not inherently positive or negative, but we flag it for visibility.
      // If there's a description of the breaking change, it's better.
      if (body.length > 100 && BREAKING_PATTERN.test(body)) {
        signals.push({
          name: 'breaking change documented',
          positive: true,
          weight: 0.8,
        });
      } else {
        signals.push({
          name: 'breaking change mentioned but not detailed',
          positive: false,
          weight: 0.8,
        });
      }
    }

    // TODOs/FIXMEs in description suggest unfinished work
    const todoMatches = body.match(TODO_PATTERN);
    if (todoMatches) {
      signals.push({
        name: `unfinished markers in description (${todoMatches.length})`,
        positive: false,
        weight: 0.6,
      });
    }

    // --- Type-specific signals ---

    if (event.type === 'issue') {
      if (/\b(steps?\s+to\s+reproduce|reproduction|repro\s+steps?)\b/i.test(body)) {
        signals.push({
          name: 'has reproduction steps',
          positive: true,
          weight: 1.3,
        });
      }

      if (/\b(expected|actual)\s+(behavior|behaviour|result|output)\b/i.test(body)) {
        signals.push({
          name: 'has expected/actual behavior',
          positive: true,
          weight: 1.2,
        });
      }

      if (
        /\b(version|environment|os|platform|browser|node|python|java|rust|go)\s*[:\d]/i.test(body)
      ) {
        signals.push({
          name: 'has environment details',
          positive: true,
          weight: 1,
        });
      }

      if (/\b(stack\s*trace|traceback|error|exception|panic)\b/i.test(body)) {
        signals.push({
          name: 'includes error output',
          positive: true,
          weight: 0.8,
        });
      }

      // Template usage detection (common issue template markers)
      if (/\b(describe the bug|feature request|is your feature request related to)\b/i.test(body)) {
        signals.push({
          name: 'uses issue template',
          positive: true,
          weight: 0.6,
        });
      }
    }

    if (event.type === 'pull_request') {
      if (/\b(fix(es)?|clos(es|ing)|resolv(es|ing))\s+#\d+/i.test(body)) {
        signals.push({ name: 'links to issue', positive: true, weight: 1.3 });
      }

      if (/\b(test\s*(plan|strategy|coverage)|how\s+to\s+test|testing|tested\s+by)\b/i.test(body)) {
        signals.push({ name: 'has test plan', positive: true, weight: 1.2 });
      }

      // Migration or upgrade guide
      if (/\b(migration|upgrade|breaking).*(guide|instruction|step)/i.test(body)) {
        signals.push({
          name: 'has migration guide',
          positive: true,
          weight: 1,
        });
      }

      // Before/after comparison
      if (/\b(before|after)\b/i.test(body) && /\b(before|after)\b/gi.test(body)) {
        const beforeAfter = body.match(/\b(before|after)\b/gi);
        if (beforeAfter && beforeAfter.length >= 2) {
          signals.push({
            name: 'has before/after comparison',
            positive: true,
            weight: 0.7,
          });
        }
      }
    }

    // Shared: references to other issues/PRs
    const refs = body.match(/#\d+/g);
    if (refs && refs.length > 0) {
      signals.push({
        name: `references ${refs.length} issue(s)/PR(s)`,
        positive: true,
        weight: 0.6,
      });
    }

    // Screenshots or images
    if (/!\[.*\]\(.*\)/.test(body) || /<img\s/i.test(body)) {
      signals.push({
        name: 'has images/screenshots',
        positive: true,
        weight: 0.8,
      });
    }

    // --- Weighted scoring ---

    if (signals.length === 0) {
      return {
        impact: 'neutral',
        confidence: 0.1,
        reasoning: 'No quality signals detected.',
      };
    }

    const positiveWeight = signals.filter((s) => s.positive).reduce((s, x) => s + x.weight, 0);
    const negativeWeight = signals.filter((s) => !s.positive).reduce((s, x) => s + x.weight, 0);

    let impact: AnalysisResult['impact'];
    if (positiveWeight > negativeWeight * 1.2) {
      impact = 'positive';
    } else if (negativeWeight > positiveWeight * 1.2) {
      impact = 'negative';
    } else {
      impact = 'neutral';
    }

    const totalWeight = positiveWeight + negativeWeight;
    const confidence = Math.min(
      1,
      (Math.abs(positiveWeight - negativeWeight) / Math.max(totalWeight, 1)) * 0.5 + 0.2
    );

    const reasoning = `Quality: ${signals.map((s) => `${s.positive ? '+' : '-'} ${s.name}`).join(', ')}.`;

    return { impact, confidence, reasoning };
  }
}