gai/src/prompt.ts

import type { PRContext, ProjectContext } from "./types";

// ── Commit System Prompt ──────────────────────────────────────────────

export const SYSTEM_PROMPT = `You are an expert at writing concise, meaningful git commit messages following the Conventional Commits specification.

Format: <type>(<scope>): <description>

Types: feat, fix, docs, style, refactor, perf, test, build, ci, chore, revert

Rules:
1. Use imperative mood in description (e.g., "add feature" not "added feature")
2. Keep the first line (subject) under 72 characters
3. Scope is optional but recommended when the change area is clear
4. For breaking changes, add "!" after the scope: feat(scope)!: description
5. If the change needs explanation, add a body separated by a blank line — explain WHY, not WHAT
6. Match the language and style of recent commits if provided
7. Be specific — avoid vague messages like "update code" or "fix bugs"
8. Output ONLY the commit message text, no markdown, no code blocks, no prefixes`;

export function buildPrompt(context: ProjectContext): string {
  const parts: string[] = [];

  if (context.packageDescription || context.readme || context.structure) {
    parts.push("## Project Context");
    if (context.packageDescription) parts.push(`Description: ${context.packageDescription}`);
    if (context.structure) parts.push(`Structure: ${context.structure}`);
    if (context.readme) parts.push(`README:\n${context.readme}`);
    parts.push("");
  }

  if (context.recentCommits.length > 0) {
    parts.push("## Recent Commits (for style reference)");
    for (const c of context.recentCommits) parts.push(c);
    parts.push("");
  }

  parts.push("## Staged Changes");
  parts.push("```diff");
  parts.push(context.diff);
  parts.push("```");
  parts.push("");
  parts.push("Generate a commit message for the above changes.");

  return parts.join("\n");
}

// ── PR System Prompt ───────────────────────────────────────────────────

export const PR_SYSTEM_PROMPT = `You are an expert at writing clear, concise pull request titles and descriptions.

Format:
<pr title>
<blank line>
<pr body>

Rules:
1. Title must be under 72 characters, in imperative mood
2. Follow the Conventional Commits style for the title (e.g., "feat(api): add user authentication")
3. Body should be 2-3 sentences in plain text explaining WHAT was changed and WHY
4. Be specific — avoid vague messages
5. Match the language and style of recent commits if provided
6. If the branch name hints at the type (e.g., "feat/..." or "fix/..."), reflect that in the title
7. Output ONLY the PR text — no markdown, no code blocks, no prefixes`;

export function buildPRPrompt(context: PRContext): string {
  const parts: string[] = [];

  if (context.packageDescription || context.readme || context.structure) {
    parts.push("## Project Context");
    if (context.packageDescription) parts.push(`Description: ${context.packageDescription}`);
    if (context.structure) parts.push(`Structure: ${context.structure}`);
    if (context.readme) parts.push(`README:\n${context.readme}`);
    parts.push("");
  }

  parts.push("## Branch Info");
  parts.push(`Branch: ${context.branchName}`);
  parts.push(`Target base: ${context.baseBranch}`);
  parts.push("");

  if (context.branchCommits.length > 0) {
    parts.push("## Commits on This Branch");
    for (const c of context.branchCommits) parts.push(c);
    parts.push("");
  }

  parts.push("## Changes (diff from base)");
  parts.push("```diff");
  parts.push(context.diff);
  parts.push("```");
  parts.push("");
  parts.push("Generate a pull request title and brief body for the above changes.");

  return parts.join("\n");
}

// ── Explain Prompt ─────────────────────────────────────────────────────

export const EXPLAIN_SYSTEM_PROMPT = `You are an expert software engineer explaining code changes in plain, accessible language.

Given a git diff, explain:
1. WHAT changed at a high level (1 sentence summary)
2. WHY these changes matter (what problem they solve or what they enable)
3. A brief breakdown of the key changes (bullet points, one per file/module)

Rules:
- Be concise but thorough
- Use plain language suitable for both junior and senior engineers
- Focus on the intent and impact, not just restating the diff
- Do NOT use markdown headings (no ##, ###). Use bold text markers like **Section:** instead.
- Keep each bullet point to 1-2 lines
- If the diff is trivial, say so and keep the explanation short`;

export function buildExplainPrompt(diff: string): string {
  const parts: string[] = [];
  parts.push("## Changes to Explain");
  parts.push("```diff");
  parts.push(diff);
  parts.push("```");
  parts.push("");
  parts.push("Explain these changes in plain language as described.");
  return parts.join("\n");
}

// ── Review Prompt ──────────────────────────────────────────────────────

export const REVIEW_SYSTEM_PROMPT = `You are a senior software engineer performing a thorough but friendly code review.

Review the following code changes and provide feedback in these categories:
1. **Bugs & Logic Errors** — actual bugs, off-by-one errors, null safety, edge cases
2. **Code Quality** — readability, naming, duplication, complexity
3. **Performance** — inefficient patterns, unnecessary allocations, N+1 queries
4. **Security** — injection risks, exposed secrets, unsafe operations
5. **Suggestions** — concrete improvements with code snippets where helpful

Rules:
- Be constructive, not harsh. Use "consider" and "suggest" instead of "you should".
- Prioritize by severity. Mention critical issues first.
- If the code looks great, say so! Don't fabricate issues.
- Keep feedback actionable — every issue should have a clear suggestion.
- Use **bold** for section headers and \`code\` for code references.
- Do NOT output a concluding summary paragraph. End with the last suggestion.`;

export function buildReviewPrompt(diff: string, strictness: "lenient" | "normal" | "strict"): string {
  const strictnessHints: Record<string, string> = {
    lenient: "Focus only on major issues. Skip minor style nits.",
    normal: "Provide balanced feedback covering all categories.",
    strict: "Be thorough. Flag even minor issues and style inconsistencies.",
  };

  const parts: string[] = [];
  parts.push(`Review strictness: ${strictnessHints[strictness]}`);
  parts.push("");
  parts.push("## Code Changes to Review");
  parts.push("```diff");
  parts.push(diff);
  parts.push("```");
  parts.push("");
  parts.push("Please review the above changes.");
  return parts.join("\n");
}

// ── Changelog Prompt ───────────────────────────────────────────────────

export const CHANGELOG_SYSTEM_PROMPT = `You are an expert at writing clear, user-facing changelogs from git commit history.

Given a list of commits, generate a changelog organized by type:
- **Features** (feat commits)
- **Bug Fixes** (fix commits)
- **Improvements** (refactor, perf, style commits)
- **Documentation** (docs commits)
- **Chores & Maintenance** (chore, build, ci, test commits)

Rules:
- Group by type, with the heading in **bold**
- Each entry should be a single line describing the change in user-friendly language
- Translate technical commit messages into language a user would understand
- Skip merge commits and trivial chore commits if they don't add value
- If a type has no entries, omit that section
- Output ONLY the changelog text, no preamble or markdown code blocks`;

export function buildChangelogPrompt(commits: string[], from?: string, to?: string): string {
  const parts: string[] = [];
  const range = from ? `from ${from}${to ? ` to ${to}` : " to HEAD"}` : "";
  parts.push(range ? `Generate a changelog for commits ${range}.` : "Generate a changelog from the following commits.");
  parts.push("");
  parts.push("## Commits");
  for (const c of commits) parts.push(c);
  parts.push("");
  parts.push("Generate a changelog from these commits.");
  return parts.join("\n");
}

// ── Suggest Prompt ─────────────────────────────────────────────────────

export const SUGGEST_SYSTEM_PROMPT = `You are an expert at suggesting git branch names and commit types based on code changes.

For branch name suggestions:
- Use format: <type>/<short-description>
- Types: feat, fix, refactor, docs, chore, perf, test
- Description should be 2-4 hyphenated words
- Provide exactly 3 suggestions, one per line

For commit type suggestions:
- Return exactly one Conventional Commit type that best matches the changes
- Valid types: feat, fix, docs, style, refactor, perf, test, build, ci, chore, revert
- Output ONLY the type name`;

export function buildSuggestBranchPrompt(diff: string): string {
  const parts: string[] = [];
  parts.push("## Changes");
  parts.push("```diff");
  parts.push(diff);
  parts.push("```");
  parts.push("");
  parts.push("Suggest 3 branch names for these changes. Output one per line, no numbering.");
  return parts.join("\n");
}

export function buildSuggestTypePrompt(diff: string): string {
  const parts: string[] = [];
  parts.push("## Changes");
  parts.push("```diff");
  parts.push(diff);
  parts.push("```");
  parts.push("");
  parts.push("What Conventional Commit type best describes these changes? Output ONLY the type name.");
  return parts.join("\n");
}