Add API cost tracking to admin dashboard

Track estimated Anthropic API costs per request across all Claude API
call sites (recommender, analyze, artist-dive, generate-playlist, crate,
rabbit-hole, playlist-fix, timeline, compatibility). Log token usage and
estimated cost to the app logger. Aggregate costs in admin stats endpoint
and display total/today costs and token usage in the admin dashboard.

backend/app/api/endpoints/admin.py

@@ -1,5 +1,6 @@
 import logging
 import io
+import re
 from datetime import datetime, timezone, timedelta
 
 from fastapi import APIRouter, Depends, HTTPException, Query
@@ -113,6 +114,28 @@ async def get_stats(
         for row in user_stats_result.all()
     ]
 
+    # Calculate API costs from log buffer
+    total_cost = 0.0
+    today_cost = 0.0
+    total_tokens_in = 0
+    total_tokens_out = 0
+    for log in _log_buffer:
+        if 'API_COST' in log.get('message', ''):
+            msg = log['message']
+            cost_match = re.search(r'cost=\$([0-9.]+)', msg)
+            if cost_match:
+                c = float(cost_match.group(1))
+                total_cost += c
+                # Check if today
+                if log['timestamp'][:10] == now.strftime('%Y-%m-%d'):
+                    today_cost += c
+            input_match = re.search(r'input=(\d+)', msg)
+            output_match = re.search(r'output=(\d+)', msg)
+            if input_match:
+                total_tokens_in += int(input_match.group(1))
+            if output_match:
+                total_tokens_out += int(output_match.group(1))
+
     return {
         "users": {
             "total": total_users,
@@ -131,6 +154,12 @@ async def get_stats(
             "saved": saved_recs,
             "disliked": disliked_recs,
         },
+        "api_costs": {
+            "total_estimated": round(total_cost, 4),
+            "today_estimated": round(today_cost, 4),
+            "total_input_tokens": total_tokens_in,
+            "total_output_tokens": total_tokens_out,
+        },
         "user_breakdown": user_breakdown,
     }
 

backend/app/api/endpoints/compatibility.py

@@ -1,6 +1,9 @@
 import json
+import logging
 
 import anthropic
+
+api_logger = logging.getLogger("app")
 from fastapi import APIRouter, Depends, HTTPException
 from pydantic import BaseModel
 from sqlalchemy import select
@@ -144,6 +147,12 @@ Return ONLY the JSON. Include exactly 5 recommendations."""
         messages=[{"role": "user", "content": prompt}],
     )
 
+    # Track API cost (Haiku: $0.80/M input, $4/M output)
+    input_tokens = message.usage.input_tokens
+    output_tokens = message.usage.output_tokens
+    cost = (input_tokens * 0.80 / 1_000_000) + (output_tokens * 4 / 1_000_000)
+    api_logger.info(f"API_COST|model=claude-haiku|input={input_tokens}|output={output_tokens}|cost=${cost:.4f}|user=system|endpoint=compatibility")
+
     try:
         text = message.content[0].text.strip()
         if text.startswith("```"):

backend/app/api/endpoints/playlist_fix.py

@@ -1,6 +1,9 @@
 import json
+import logging
 
 import anthropic
+
+api_logger = logging.getLogger("app")
 from fastapi import APIRouter, Depends, HTTPException
 from pydantic import BaseModel
 from sqlalchemy import select
@@ -114,6 +117,12 @@ Return ONLY the JSON object."""
         messages=[{"role": "user", "content": prompt}],
     )
 
+    # Track API cost (Haiku: $0.80/M input, $4/M output)
+    input_tokens = message.usage.input_tokens
+    output_tokens = message.usage.output_tokens
+    cost = (input_tokens * 0.80 / 1_000_000) + (output_tokens * 4 / 1_000_000)
+    api_logger.info(f"API_COST|model=claude-haiku|input={input_tokens}|output={output_tokens}|cost=${cost:.4f}|user={user.id}|endpoint=playlist_fix")
+
     response_text = message.content[0].text.strip()
     # Handle potential markdown code blocks
     if response_text.startswith("```"):

backend/app/api/endpoints/recommendations.py

@@ -250,6 +250,12 @@ Return ONLY the JSON object."""
         messages=[{"role": "user", "content": prompt}],
     )
 
+    # Track API cost (Haiku: $0.80/M input, $4/M output)
+    input_tokens = message.usage.input_tokens
+    output_tokens = message.usage.output_tokens
+    cost = (input_tokens * 0.80 / 1_000_000) + (output_tokens * 4 / 1_000_000)
+    api_logger.info(f"API_COST|model=claude-haiku|input={input_tokens}|output={output_tokens}|cost=${cost:.4f}|user={user.id}|endpoint=artist_dive")
+
     response_text = message.content[0].text.strip()
     if response_text.startswith("```"):
         response_text = response_text.split("\n", 1)[1]
@@ -346,6 +352,12 @@ Return ONLY the JSON object."""
         messages=[{"role": "user", "content": prompt}],
     )
 
+    # Track API cost (Haiku: $0.80/M input, $4/M output)
+    input_tokens = message.usage.input_tokens
+    output_tokens = message.usage.output_tokens
+    cost = (input_tokens * 0.80 / 1_000_000) + (output_tokens * 4 / 1_000_000)
+    api_logger.info(f"API_COST|model=claude-haiku|input={input_tokens}|output={output_tokens}|cost=${cost:.4f}|user={user.id}|endpoint=generate_playlist")
+
     response_text = message.content[0].text.strip()
     if response_text.startswith("```"):
         response_text = response_text.split("\n", 1)[1]
@@ -464,6 +476,12 @@ Only recommend real songs. Return ONLY the JSON array."""
         messages=[{"role": "user", "content": prompt}],
     )
 
+    # Track API cost (Haiku: $0.80/M input, $4/M output)
+    input_tokens = message.usage.input_tokens
+    output_tokens = message.usage.output_tokens
+    cost = (input_tokens * 0.80 / 1_000_000) + (output_tokens * 4 / 1_000_000)
+    api_logger.info(f"API_COST|model=claude-haiku|input={input_tokens}|output={output_tokens}|cost=${cost:.4f}|user={user.id}|endpoint=crate")
+
     response_text = message.content[0].text.strip()
     if response_text.startswith("```"):
         response_text = response_text.split("\n", 1)[1]
@@ -598,6 +616,12 @@ Only use real songs. Return ONLY the JSON."""
         messages=[{"role": "user", "content": prompt}],
     )
 
+    # Track API cost (Haiku: $0.80/M input, $4/M output)
+    input_tokens = message.usage.input_tokens
+    output_tokens = message.usage.output_tokens
+    cost = (input_tokens * 0.80 / 1_000_000) + (output_tokens * 4 / 1_000_000)
+    api_logger.info(f"API_COST|model=claude-haiku|input={input_tokens}|output={output_tokens}|cost=${cost:.4f}|user={user.id}|endpoint=rabbit_hole")
+
     response_text = message.content[0].text.strip()
     if response_text.startswith("```"):
         response_text = response_text.split("\n", 1)[1]

backend/app/api/endpoints/timeline.py

@@ -106,6 +106,13 @@ Return ONLY a valid JSON object with "decades" and "insight" keys. No other text
             messages=[{"role": "user", "content": prompt}],
         )
 
+        # Track API cost (Haiku: $0.80/M input, $4/M output)
+        api_logger = logging.getLogger("app")
+        input_tokens = message.usage.input_tokens
+        output_tokens = message.usage.output_tokens
+        cost = (input_tokens * 0.80 / 1_000_000) + (output_tokens * 4 / 1_000_000)
+        api_logger.info(f"API_COST|model=claude-haiku|input={input_tokens}|output={output_tokens}|cost=${cost:.4f}|user={user.id}|endpoint=timeline")
+
         response_text = message.content[0].text.strip()
 
         # Try to extract JSON if wrapped in markdown code blocks